Pre-Intermediate · Grammar Reference
Unit 8 — Modal Verbs
have to · modals overview · should · must
8.1 have to
Form
| + | – | ? |
|---|
| I / you / we / they | have to go | don't have to go | Do you have to go? |
| he / she / it | has to go | doesn't have to go | Does she have to go? |
| Past | had to go | didn't have to go | Did you have to go? |
Use
- Obligation / necessity (external): I have to wear a uniform at work.
- No obligation (negative): You don't have to come. (= not necessary, not prohibited)
8.2 Modal auxiliary verbs
Modal verbs are followed by the bare infinitive. They have no -s in the third person and no auxiliaries in negatives/questions.
| Modal | Use |
|---|
| can | ability, permission, possibility |
| could | past ability, polite request |
| will | future, offers, promises |
| would | conditional, polite request |
| should | advice, recommendation |
| must | strong obligation, logical deduction |
| might | possibility (less certain than may) |
| may | possibility, polite permission |
8.3 should
Form
You should see a doctor. You shouldn't eat so much sugar.Use
- Advice: You should get more sleep.
- Recommendation: You should try the pasta here.
- Mild obligation / expectation: Students should arrive on time.
8.4 must
Form
I must finish this. You mustn't be late.Use
- Strong obligation (internal/speaker): I must remember to call her.
- Prohibition (mustn't): You mustn't smoke here.
- Logical deduction: She's not here — she must be sick.
📌 Note
must vs have to: must = personal obligation;
have to = external obligation.
mustn't = not allowed;
don't have to = not necessary (but allowed).